Approach control in coded track circuit signaling systems



March 4, 1952 J. Y. HOWARD APPROACH CONTROL IN CODED TRACK CIRCUIT SIGNALING SYSTEMS 4 SheecQs-Sheet 1 Filed June 16, 1945 March 4, 1952 J. Y. HOWARD 2,588,005

APPROACH CONTROL IN CODED TRACK CIRCUIT SIGNALING SYSTEMS 4 Sheets-Sheet" 2 Filed June 16, 1945 Imnemtor 1 Cttformeg March 4, 1952 J, HOWARD 2,588,005

APPROACH CONTROL IN CODED TRACK CIRCUIT SIGNALING SYSTEMS Filed June 16, 1945 4 Sheets-Sheet 5 Manila 4, 1952 J Y HOWARD 2,588,005

APPROACH CONTROL IN CODED TRACK V CIRCUIT SIGNALING SYSTEMS Fiied June 16, 1945 v 4 Sheets-Sheet 4 FIG. 6. I

- (Ittorneg Patented Mar. 4, 1952 UNITED STATES PATENT 1 APPROACH CONTROL IN CODED TRACK CIRCUIT SIGNALING SYSTEMS James Y. Howard, Greece, N. Y., assignor to General Railway Signal Company, Rochester,

19 Claims. 1

The present invention relates to automatic block signalling systems for railroads using coded track circuits, and more particularly pertains to improved means for providing approach control in such signalling systems.

The conventional block signalling system having coded track circuits provides that impulses of currentpare supplied to the exit end of each coded track circuit section with spaced intervals, between the impulses which have been conveniently termed off periods. These timespaced impulsescomprise a driven code, and are applied to the exit endof each section at different distinctive code rates in accordance with the traflic conditionsin advance of that section.

At the entrance end of each conventional coded track circuit section, a code following track relay is connected acrossthe rails of that section toreceive the driven code impulses, and act upon suitable decoding apparatus which is distinctively controlled in accordance with the rate of the driven code received. This decoding apparatus acts to govern the indications of the as sociated signal in accordance with trafiic conditionsin advance of that signal, and also to select the, code rate to be applied to the next tracksection in the rear.

In such an, automatic block signalling system, it is often desirable to provide what is known as approach control, which may be employed for various purposes, such as approach lightingthe signals. approach control of highway crossings, or, approach locking control. It has been, previously proposed that such approach control may be provided by using what is known as a shunt relay, i, e. a relay connected acrossthe track rails at the leaving end of a section which acts to follow the applied driven code impulses, but is prevented from acting when, the associated sec tion is occupied and shunted by a train. Another form of approach control proposes to use a series relay governed in accordance with the current of the applied code impulses, and this current applied to the track rails is sufficient to operate the series relay only if the associated sectionis occupied by a train. In both of these proposed arrangements the variations in cur-- rent and. voltage due to changes in the potential of thetrack source. of energy, and the like, some times render such approach track relays inefiective to indicate an approaching train over the desired approach distance.

Another difficulty experienced with the use of approach track relays of the above type, is that the difference in code rate applied to the track rails changes the sensitivity of such approach ro lays, thus changin the distance over which they will reliably act to detect the presence of an ap proaching train under different traffic conditions.

In viewof the above considerations, it is pro posed in accordance with the present invention to provide means for compensating for various changeable conditions encountered in practice which will render the approach relays more uniform in their operation and more sensitiv to the presence of a train in their associated track sections.

Generally speaking, and without attempting to define the exact nature or scope of the present invention, it is proposed to provide an approach relay which is governed in accordance with the driven code pulses applied to the eXit endof a track sectionso as to be responsive to the presence of a train entering that track; section, but provided with compensating means for changing the electrical characteristics or the approach relay in accordance with changes in the potential of the source of energy supplying the current for the driven code pulses, and also in accordance with the changes in thedifferenttcode rates selected for the driven code pulses.

In providing compensation for an approach relay under the conditions above described, it is proposed in connection with the preferred form of the invention to effect such compensation by the use of an auxiliary compensatin winding-on the approach relay controlled in a manner to increase the inherent sensitivity of the approach relay organization, so that the approach control provided by such an organization will extend over a track section of increased length as compared to those used in connection with the conventional approach relays.

More specifically, it is proposed that a twoposition biased polar relay will be provided with an operating winding and an auxiliary compensating winding. The main winding is governed in accordance with either the potential or the current supplied to the track rails by the application of the driven code pulses tothe corresponding end of the track section; while, the auxiliary winding is supplied with energy of a lesser degree'but creating a magnetic flux in the relay in opposition to the magnetic flux produced by the energization'of the main winding. With this organization, any particular percentage of change in the energization of the main winding of, the approach relay due to the entrance of a train into the associated track section will have a, much greater eifect upon the net operating magnetic flux of the relay, because the net operating flux of the relay is only a part of the flux produced by the main winding. This character: istic functioning of the present invention thus provides a more sensitive approach control organiz ation.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings, and in part pointed out as the description of the invention progresses.

In describing the present invention in detail, reference will be made to the accompanying drawings, in which:

Fig. 1 shows one form of the present invention having an improved shunt type approach relay organization Fig. 2 shows another form of the present invention having an improved series type approach relay organization;

Fig. 3 shows a modified form of Fig. 1 including an improved form of compensation in connection with a shunt type approach relay for changes in the potential used for the driven code pulses when a shift is made from a source of rectified alternating current to a reserve battery source upon failure of the alternating current;

Fig. ,4 shows a simplification of the organization of Fig. I particularly illustrating compensation in shunt type approach relay for changes in the selected driven code rate; v Fig. 5 shows a simplified form of shunt type approach relay with compensation for changes in the driven code rate; and

Fig. 6 shows a simplified form of series type approach relay having compensation applied thereto for changes in the driven code rate.

For the purpose of simplifying the illustration,

and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawing having been made more with the purpose of making it easy to understand the principles and mode of operation than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a conventional manner, and symbols are used to indicate connections to the terminals of batteries or other suitable sources of electric current instead of showing all of the wiring connections to these terminals. The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of direct current, and the circuits with which these symbols are employed are assumed to always have current flowing in the same direction, although it is to be understood that in some cases alternating current might be substituted for the direct current, if desired, and in such cases the and are to be considered as indicating the relative instantaneous polarities of the alternating current. Although symbols are employed in various cases, in certain instances the batteries and their associated connections are shown.

4 entrance ends of the track sections T2 and T3 respectively. These signals can of course be of any other suitable type desired.

At the exit end of the track section T2, code transmitting apparatus has been shown as including a code transmitting relay CP which, when actuated to an operated position, connects a source of energy across the track rails of section T2 through front contact 6 and including an adjustable series resistor 1. But when the code transmitting relay CP is deenergized and back contact 6 is closed, a shunt circuit including wire 8 shunts the track rails of section T2 to dissipate any stored energy in the track rails due to socalled storage battery action.

The code transmitting relay CP has its contact 6 operated to opposite positions alternately due to the successive time spaced energizations of this relay in accordance with the '75 or 180 code rate as selectively determined by the decoding apparatus associated with signal S3. This decoding apparatus at signal S3 has merely'beenfindicated as including a code following track relay TR3 of the biased polar type which acts in turn to control the home and distance relays 'HR3 and DB3 in any suitable conventional way well known in the art. One such Way of controlling these relays has been shown in detail in the prior application of F. X. Rees, Ser. No. 500,662, filed August 31, 1943 which has'resulted in Patent No. 2,378,325, dated June 12, 1945. It should be understood, however, that regardless of the particular type of decoding apparatus associated at signal S3, similar apparatus will be associated with signal S2 and the other signals of the stretch of track to which the block signalling system is applied.

In this connection, it is sufficient for an understanding of the present invention to know that the relay HR3 is picked up due to the reception of code impulses of either the '75 or 180 code rates from the exit end of track section T3. When the relay HR3 is picked up and closes its front contact 9, the coding contacts IC are effective to intermittently energize the code transmitting relay CP at the 180 code rate; whereas if the relay HR3 is deenergized due to the presence of a train in the track section T3, for example, then back contact 9 is closed and the relay CP is energized from the coding contacts at the 75 code rate. These coding contacts IBM) and 150 may be of any suitable type, that is, they may be motor driven, or may be code oscillators of the type disclosed, for example in the prior Patent No. 2,351,588, granted to O. S. Field, June 20, 1944. The coding contacts C and 150 are assumed to produce 180 code impulses per minute and 75 code impulses per minute respectively, although it is to be understood that different code rates may be employed, if desired.

The decoding apparatus causes the distant relay, such as relay DR3 to be picked up only'when the 180 code rate is received by the code following relay TR3. Thus, when the 180 code rate is received front contacts 10 and H of relays HR3 and DB3 are closed for preparing an energizing circuit for the green or proceed lamp G of the signal 53, which is energized when a train is in approach to signal S3 by reason of the deenergization of the approach repeater relay AR2 in a manner later to be explained, and the closure of back contact l2. On the other hand, if a 75 code rate is being received then the relay DB3 is dropped away and back contact I I is closed so that the yellow or caution lamp Y of signal S3 is energized assuming the back contact [2 to be closed because of an approaching train.

In the event that the code following relay TR3 fails to receive any code whatsoever, due to a train being in the track section T3, a broken rail, or the like, then both of the relays I-IR3 and DB3 are deenergized closing back contact It so that the red or stop lamp R of the signal S3 is energized upon the approach of a train and the closure of back contact 12.

The operation of the code transmitting relay CP, as above mentioned, closes front contact 6 for each impulse to connect the track source of energy in series with the adjustable series resistor l to apply a code pulse across the rails of the track section T2. Each application of a driven code pulse to the track rails at the exit end of the track section T2 effects theoperation of ,the code following track relay TRZ at the entrance end of that track section. The operation of this code following track relay 'IRZ in accordance with the particular code rate applied at the exit end, causes the operation of the associated decoding apparatus including the home relay HRZ and distant relay DRZ to effect the control of the signal S2 in a manner similar to that already described in connection with signal S3. This decoding apparatus also acts to select the code rate applied to the next track section TI inthe rear, as well as effecting certain compensating functions, as will be later described more particularly in connection with the apparatus associated with signal S3. The approach repeater relay ARI is controlled in the same manner as the relay AR2 associated with signal S3.

The source of track energy at the exit end of each track section, such as at the exit end of track section T2, includes a source of alternating current connected to a step-down transformer I3 having its secondary winding connected through a full-wave rectifier unit I4 supplying rectified alternating current in multiple with a track battery 5. This track battery 5 may be of any suitable type storage battery, or maybe a suitable type primary battery. In the first case, the organization then takes the form commonly known as a trickle charge arrangement with the storage battery 5 normally supplied with potential from the rectifier unit sufficient to keep it fully charged. In this case, the load is normally supplied by the rectified alternating current, but

in the event of a power failure, the storage battery 5 immediately carries the load at slightly reduced potential.

In the second case, where the battery 5 is a primary type battery, such as a caustic soda Edison battery, the rectified alternating current source supplies such a potential to the primary battery 5 so as to be below the normal no-loacl voltage of the battery but above the load carrying voltage of the battery. This is so that the rectified alternating current potential will not be higher than the inherent voltage characteristics of, the primary battery and cause damage to. the battery; while yet being sufliciently high as to normally carry the load while the alternating current supply is present. On the other hand, if there is a failure in the alternating current supply, then the primary battery takes over the load and supplies it at potential in accordance with the characteristics of such a battery. More specific consideration will be given to the different voltage characteristics of the track sources of energy as the description progresses.

Across the secondary, Winding of the transformer I3 is connected an alternating; current power-off relay PO-which is picked up so long'as the alternating current power supply is present, but in the event of power failure this relay PO drops away.

Inthis form of the invention shown in Fig. 1, an approach shunt type relay SH of the polar biased type is shown as having an upper main winding connected across the track rails through a serie resistor [5. Each time a code pulse is applied to the track rails this relay SH has its upper winding energized so that its contact I6 is picked up which in turn energizes the relay ARZ. Since this shunt relay SH follows the particular code applied to the track section T2, the relay ARZ is intermittently energized, but it is suificiently slow acting as to remain picked up between successive energizations. Whenever the shunt relay SH becomes steadily deenergized and fails to follow any code, due to the presence of a train in the track section T2 or due to other causes, the relay AR2 drops away and closes its back contact l2 to effect the illumination of the signal S3 as previously described. In this connection, it should of course be understood that the relay ARZ may be employed in connection with the approach controlling of highway crossing signals, approach looking, or the like, and

still be within the scope of the present invention.

While the alternating current supply is present and effectivelymaintains the power-off relay PO picked up, a circuit including front contact I! of relay PO and a series resistor I8 of the adjustable type-acts to connect the lower auxiliary winding of the relay SH across the opposite terminals of the battery 5 and the rectifier unit M. It is noted that the flow of energy in the lower auxiliary winding of relay SH causes a magnetic flux which opposes the magnetic flux produced by the flow of energy in the upper main winding of relay SH as indicated by the arrows within the respective windings.

Under the above conditions, it is assumed that the adjustable resistor l is so set as to properly 1 supply energy to the code following trackrelay 'IRZ under the existing possible variations in ballast conditions, and also to supply the energy for the upper winding of relay SH which is directly connected across the trackrails of section T2 in series with the adjustable resistor l'5. The adjustable resistor 58 is so set that the current flow in the auxiliary compensating winding of the relay SH for the existing potential across the terminals of the battery 5 will create a magnetic flux to oppose the magnetic flux produced in the main operating winding of the relay SH to the proper extent to give the desired net operating flux-value so that the entrance of a train into the section T2 as it passes the signal S2 will cause the relay SH to remain dropped away although driven code pulses continue to be applied to the rails by relay CP. This of course assumes that the power-off relay PO is picked, up and that the potential of the track power supply is actually provided by therectified alternating current.

Under the conditions just described, the coding apparatus is assumed to be operating at the code rate because the relay HRB is picked up closing its front contact 9. But since the power required to operate the armature and contacts of relay SH at this 180 code rate is greater than that power required to operate it at the slower 75 code rate, it will be apparent that compensation, should. be made forsuch a change in rate.

fighting signal S3.

7 This is accompilshed by the relay HR3 when it drops away to close back contact 9 and change the code rate, by also closing the back contact I 9 so as to connect the adjustable resistor in multiple with the resistor l8 when the '75 code rate is being applied. This reduces the resistance of the circuit for the lower compensating winding of the relay SH, and results in its increased energization to give the relay SH a proper net operating magnetic flux so that the relay will have the same sensitivity of response to the entrance of a train into the track section T2 under the low code rate as it had for the high code rate. In other words, the net operating flux of the relay SH is of one particular value while the 180 code rate is being applied to the track section T2 by the transmitting relay CP, but such net operating value of magnetic flux is reduced during the operation of the relay CP by the '75 code rate. Although this compensation for a change in code rates has been shown with respect to only two difierent rates, it should be understood that the same principles of compen sation may be applied for any desired number of different code rates. 1

Regardless of whether the '180 or 75 code rate is being applied to the track section T2, each of the code pulses acts to operate the code following track relay TRZ at the entrance end and the approach relay SH at the exit end. As above andis deenergized between the code pulses regardless of the rate then selected.

When a train enters a track section T2, the shunt effect of the train reduces the resistance of the track circuit so that increased current flows through the adjustable resistor 1 and such current causes a potential drop across such resistor I which acts to reduce the potential applied to the track circuit. This reduction in potential across the track rails of the track circuit, and the potential drop in the track rails themselves .results in the effective shunting of the track relay TRZ so that it stops operation. The reduction in the potential applied across the track rails at the exit end also results in a reduction of the effective energization of the upper winding of the shunt relay SH whereas the lower or compensating winding of the relay SH is maintained energized at the same value directly from the track source of energy. It is understood of course that only the resistor I8 is included'in the compensating circuit when the 180 code rate is being applied and that the resistor '20 is included in multiple therewith when the 75 code rate is being applied. This reduction in the energization of the upper or operating winding of the relay SH reduces the net operating flux of the relay below that value which will effect the picking up of the relay commonly known as the pick-up value. Thus, the entrance of the train into the track section T2, regardless of the code rate applied thereto causes the relay SH to cease its operation and thus allow the approach repeating relay AR2 to become deenergized closing back contact I2 and approach This condition is of course maintained as the train proceeds from the entrance of the section T2 throughout its length until it leaves the section at the right-hand end.

The approach relay SH is more sensitive in its response to the entrance of a train not only due to the fact that its net operatingvalue is so compensated as to be maintained at a proper value for different conditions, but also because of the inherent characteristics of such an organization where the approach relay has a differentially connected auxiliary winding. This can perhaps be best understood by considering certain possible operating characteristics of a relay somewhat more in detail.

In a conventional organization where the ap-. proach relay has only one winding, let us assume that its pick-up value of energization is about half of its normal operating value. It will then be readily appreciated that in order for a train to shunt such a relay and cause it to remain dropped away, the train shunt must be effective to reduce the potential applied across the track rails to at least fifty percent of its normal value.

In the present organization, let us assume that the relay SH has the same net operating magnetic fiux as the conventional relay just considered, and that the compensating winding is energized to a value equal to a normal operating value. Then the main operating winding must be energized to double the normal operating value in order to give a net resultant operating flux of a normal value. With such a set of assumed values, it will be seen that a reduction'in the potential across the track rails equal to twenty-five percent will result in a twenty-five percent reduction of the flux in the main winding, but since this twenty-five percent is with respect to the full value of existing energization of the main operating winding then the net operating flux of the relay has been reduced fifty per cent.

With this comparison, it can be seen that the differential winding provides that the net operating flux in such a relay will be reduced to a much greater extent than the actual percentage change in potential across the track rails, whereas the operating fiux in the conventional organization can never change a greater degree than the actual percentage change in interrail potential. It is to be understood that these relative values and percentages have merely been selected for the purposes of explanation, and that various combinations of operating values, pickup values and the like may be employed depending upon the circumstances of practice.

From the above brief explanation, it will be appreciated that a train shunt will be required to be less effective in connection with the present invention when such a train enters a track section, than would be required for maintaining the approach relay deenergized in a conventional organization. For this reason, the approach relay organization of the present invention may be employed with longer track sections and still provide for the desired response of the approach relay upon the entrance of trains into such track sections. On the other hand, sometimes in practice the coded track circuit sections become so long between signal locations that it is not possible to have the approach relays operate as soon as a train enters the section. In such cases, it will be appreciated that the present organization will give a much longer approach control distance than can possibly be provided by a conventional approach relay organization.

Thus far in the description, it is assumed that the alternating current power supply has been maintained, so that the power-01f relay PO remains picked up closing front contact I! and thus maintaining the energization of the compensatingwinding of the relay SH. However, it may happen that the alternating current source of energy may fail, due to a break in the power line, or other reasons, causing the relay PO to drop away and close its back contact ll to connect the voltage regulating relay VR. across the terminals of the battery 5. Immediately upon such power failure, the load ceases to be supplied by the rectified alternating current so that the battery begins to carry the load without any interruption. The potential across the battery 5 under such circumstances is usually substantially the same as if the alternating current supply were still present, and in such a case the voltage regulating relay VB is caused to pick up and close its front contact 2! to continue the energization of the compensating winding of the relay SI-I through the resistor [8.

After a time, with either a storage type battery or a primary type battery, the voltage across the battery 5 will decrease, and when this decrease has reached a predetermined amount, the voltage regulating relay VR drops away and opens the front contact 2| removing the current supplied to the compensating winding through resistor l8. In other words, the potential applied across the opposite rails of the track section T2 is reduced to such a degree that there is no need for the counter-action of the lower winding of the relay SH to maintain a proper net operat- :3.

ing magnetic flux for the relay.

It is noted that, regardless of whether the voltage of the battery 5 is high or low as indicated by the relay VR when the alternating current power supply has failed, a change in the sistor i8 is not included in the compensating winding circuit, then of course a smaller compensating current flows. In other words, the circuit including the back contact l9 and the resistor 20 are intended to compensate for the difference in energy required for the relay SH under the changes in code rates under all .conditions; while the resistor I8 is intended to compensate for a difference in terminal voltage across the battery 5.

In case battery 5 is of the storage battery type, it is observed that the potential of the battery drops off rather gradually from the terminal voltage supplied by the rectified alternating current through the rectifier unit M, so that the relay VB is preferably adjusted under such circumstances to drop away when the decrease in terminal voltage has reached a predetermined value. For this reason, the change from rectified alternating current energy supplied by the rectifier M to energy from the battery 5.1'esults in no immediate change in. voltage upon the failure of thealternating current power supply.

In case battery 5 is of the primary type, such as causticsoda battery then the terminal voltage of this battery 5 will drop away rather rapidly following the failure of the alternating current and willstabilize at what may be termed a load carrying ordischargingpotential. After the loadhas been carriedfor atime. at this dischargingzpotential, the battery potential will gradually begin to drop off until such primary battery becomes fully discharged. Although the arrangement and description of the invention disclosed in Fig. l is applicable to both storage batteries and primary batteries, it may be desirable under certain circumstances where primary batteries are employed to takeinto consideration the relatively rapid dropping of potential immediately following the failure of the alternating current power supply. For this reason, a simplified form 'of differentially connected shunt type approach relay has been shown in Fig. 3 with What may be termed a three-step compensating organization.

Referring to Fig. 3, it will be noted that the same reference characters have been applied to those devices of this figure which correspond to the same devices of Fig. 1.

In this form of the invention, the alternating current supply acts through the rectifier unit I4 to normally supply the power for the track circuit organization with the primary battery 5 floating across this rectified alternating current supply in a manner previously described. Under the normal conditions, the lower auxiliary winding of the approach relay SH is energized through front contact 30, resistor 31 and resistor 18 in series through the lower winding of relay SH. The energy which flows in this auxiliary winding creates a magnetic flux in the relay SH in opposition to the magnetic flux created by the energization of the main winding of this relay so that the net operating flux of the relay is proper for causing this relay to follow a 180 code. If the code rate is shifted to the 75 code rate then the resistor 20 is connected through back contact IS in the same manner, as described in connection with Fig. 1.

In the event that the alternating power current fails, the relay PO drops away and closes back contact to connect the relay VR across the terminals of the battery 5. This causes the relay VR to pick up and close its front contact 32and connect the resistor l8 directly in series with the compensating winding with relay SH. In other words, the resistor 3| which is included in series with the resistor [8 under normal conditions when rectified alternating current is supplied, has been excluded from the compensating circuit in anticipation that the voltage of battery 5 will. rather rapidly drop off to its normal discharge voltage, which will require the lowered resistance in the compensating circuit. The relay VB is then adjusted so as to drop away when the potential of battery 5 falls just below its lead carrying potential, and thus at such time entirely removes the voltage compensation resistors from the circuit leaving the lower winding of relay sI-I deenergized, unless the code rate is reduced to the code rate. Thus, three-step compensation for voltage changes has been provided. In this connection, it might be noted that the potential of battery 5 will rather quickly drop from its noload potential to its discharging or load carrying potential when a train ispresent in the associated track section, and for this reason the added step the compensation is especially useful in case primary batteries are employed.

Whenever a train leaves a track section, the.

load on the battery 5 is, of course, reduced and its potential may again rise to a point which will cause the relay VR to pick up both in the case-of storage batteries and in the case of primary batteries. Suchpick-up of the relay VIR will, of course,.restore the energization of ,thecompensensitivity for response to the approach of another train.

It should, of course, be understood that following a power failure, the restoration of the power will result in the reenergization of the power-01f relay PO so that it will pick up its contact I 1 and restore the normal conditions with respect to the control of the compensating winding on the relay SH.

It was pointed out above that relay SH is of the polar biased type of relay, that is, the relay armature and its associated contacts have two polar. positions, and are biased to one of those positions. The connections to the windings of the relay are so made that the energy in the compensating winding tends to move its contacts toward their biased positions, while energy in the main winding tends to actuate its contacts toward their operating positions. When the magnetic flux produced by the two windings results in a net value of flux equal to the pick-up value, and in a direction to operate the relay against its' bias, its contacts are actuated to their picked-up or operated positions. This polarization of the relay has the function of preventing false operation of the relay under certain conditions, such as when a train is adjacent the exit end of the track section and the net operating magnetic flux tends to move the contacts of the relay toward their biased positions, because, under such conditions,

the contacts of a conventional neutral relay would be falsely operated. By using the olarized relay, the contacts remain in their normal biased positions regardless of whether the compensating winding overpowers the main operating winding or not during the passage of a train through the track section T2.

Compensated series relay 0 Fig. 2.-Fig. 2 of the accompanying drawings has been shown to illustrate how a series approach track relay having the features of compensation provided by the present invention can be used in place of the shunt relay of Fig. 1. In this form of the invention those parts corresponding to the same parts in Fig. 1 have been given the same reference characters.

The same general organization is provided wherein the rectifier unit l4 normally supplies the load with the battery 5, which may be of the storage battery type or of the primary battery type, floated across the opposite terminals of the rectifier unit. Each time the code transmitting relay CP is energized, it closes front contact 6 to apply a code pulse through series resistor 1 across the rails of the track section T2. Each time the code transmitting relay CP. is deenergized, its back contact 6 closes a circuit including wire 8 for shunting the track rails.

In this form of the invention, the main winding of the series relay SR is connected in series with resistor 22 which in turn is connected across the terminals of the series resistor l. The lower or auxiliary winding of the relay SR is controlled in exactly the same way as describedin connection with Fig. 1, and in this connection it should be understood that the relay SR is of the polarized type having its contacts and armature biased ,to one particular position. Under normal conditions, the voltage drop across the series resistor T is too low to cause suflicient current flow through operation of the relay. However, when a train enters the track section-T2, it shunts the trackrails causing an increased current flow from the track energy source through the series resistor I. This increased current flow causes an increased potential drop across the series resistor I, which is sufficient to produce a considerably higher flux in the upper winding of the relay SR so that the net fiux of the relay SR is sufiicient to operate its contacts.

In other words, the relay SR is normally at rest and does not follow the code applied to the track section 22 by the operation of the code transmitting relay CP, as does the relay SH of Fig. 1. Thus, the approach repeating relay AR2 is normally deenergized and its front contact 24 is normally open. When a train enters the track section T2 and shunts the track rails to cause an increased track current to flow, a voltage drop across the resistor 1 causes suflicient current flow through the upper winding of the series relay SR to establish a net operating flux value inthe' relay. Then the series relay SR is caused to follow the code as is then being applied to the track section. This intermittent operation of the relay SR intermittently closes contact 23 to cause intermittent energization of the approach repeating relay ARZ and cause it to pick up so long as such intermittent operation is maintained. This operation occurs both during the transmission of the code and during the transmission of the 75 code.

It will be apparent that in this form of the invention the energization of the operating Winding of relay SR and the compensating winding is such as to maintain the net operating flux of the relay SR below the pick-up value of the relay under normal conditions; whereas when a train enters a track section the winding is energized to a degree that the flux produced thereby minus the flux produced by the compensating winding results in what might be termed a normal net operating value. This form of they invention gives exactly the same characteristic features of sensitivity to the approach relay under the different conditions involved as described in connection with Fig. 1. For example, the back contact IQ of relay HR3 provides for governing the degree of energization of the auxiliary winding of relay SR to compensate for changes in the code rates applied to the track section T2 by the code transmitting relay CP. Similarly, the relay VR and its associated relay PO both act to govern the auxiliary or compensating winding of the relay SR in accordance with voltage changes of the track source of energy as described in connection with Fig. 1. It should also be understood that this Fig. 2 may be similarly modified, as described in connection with Fig. 3, so as to provide what has been conveniently termed three-step voltage compensation. It is believed unnecessary to further discuss the detais of operation of Fig. 2, since they will be readily understood by analogy to the operation described in connection with Figs. 1 and 3.

With reference to Fig. 4, a simplified illustration has been shown of the differentially con- In this Fig. 4, it is assumed, as will occur un-' der some conditions" of trackway and batterysupply, that the source of "supply will be'rela-" 13 tively' stable because of the condition involved. The operation of i the code transmittingrelay 4CP at the 180 code rate through frontcontact 40 of relay 4BR, or at the '75 code rate through the back contact 4il, ca'uses the contact 4| to be intermittently operated to apply code pulses to the track rails of the track section iTthrough the series resistor 42. These pulses of course operate the code following track relay 4TB, at the. entrance end and likewise energize the main operating winding (the lower winding in this case) of relay 4SH through a resistor 43. The auxiliary (upper winding in thiscase) of relay 48H isenergizedthrough the resistor 44 directly across the opposite terminals of the track battery 45. Since the main winding (lower) of relay 48H is energized to a greater degree duringea'ch code pulse than the differential auxiliary winding, there is a net operating fiux in the relaythat'causes it to normally follow the code applied to the exit end of the track section causing its front contact 46 to be intermittently operated to cause the approach repeating relay 4'AR to be maintained picked up. It will bezobserved that this organization corresponds exactly with the organization disclosed in Fig. I withthe exception that the compensatingwind ing'is permanently connected to a source of energy through the series resistor 44. Thus, the relay 48H has a normal condition of sensitivity to the'entrance of a train into a track section for'4T while a 180 code rate is being applied to that section by the code transmitting relay 4GP.

When'the relay 4HR, drops away to shift the code transmissionfrom the 180 rate to the 75 rate, the back contact 4'! of relay ll-IR is closed connecting the resistor 48 in multiple with the resistor 44 to increase the energization of the auxiliary winding'of the shunt relay '4SH. This is to compensate for the decrease of the energy requirements of the relay 4SH in following the slower '75 code rate.

This organization thus provides for compensation for changes in code rate and also provides that the shunt relay SH is provided with a permanently energized differentially connected auxiliary winding, so that this relay has the added sensitivity characteristic of this type of organization, as previously described in connection with Figs. 1, 2 and 3.

The entrance of a train into the track section 4T shunts the track rails of that section and causes increased current to flow from the track battery 45 and through the series-resistor 42. The added potential drop which occurs in the resistor-42 results in the effective shunting of the track relay 4TB. and the approach relay 48H. Assoon as the approach repeating relay toillustrate that the principles involvedin the present inventionin compensating for changes" in therate of code transmission. maybe applied to a simple shunt relay of the more conventional form. Referring to Fig. '5, it will be seen that the code transmitting relay 5GP is energized-in- &5

simplified forniof the invention has been shown 1 termi-ttently in accordance with the 1:80 code rate while. front contact 50 of relay 5113. ist- 14 closed, but is energized at the" code rate w hen the-backlcontact 50 is closed.

Regardless of the particular rate at which the relay 5GP is energized, each time it closes the front contact 5| it causes an impulse to be applied to the rails of the track section 5T from the track battery .55 andthrough the series resistor 52. These impulses of course operate the code following track relay 5TH, as well as also supplying energy through the resistors 53 and 54 to the relay SSH while the 75 code is being applied and through only the resistor 53 while the 180 code is being applied. This is'because the front contact 51 of relay 5HR. shunts the resistor-54 while the 180 code is applied but unshunts suchresistor 54 while the 75 code is being applied.

Under normal conditions the shunt relay SSH i normally operating in response to the transmission ofcode pulses'applied to the associated track section 5T so that its'front contact 56 intermittently energizes the approach repeating relay .EAR. This relay 58H isshown as a neutral relay, but may be polarized if it is desired to improve the time characteristics of the relay. However, it should be understood that polarization of the relay is not essential in this'forrn since there is no compensating auxiliary winding.

'Whenevera train enters the track section 5T, it shunts the rails and causes an increased track circuit current to flow increasing the potential drop across the series resistor 52. This results in the decrease of the potential applied to the track relay for operating the track relay 5TH and also a decrease in the potential applied to the circuit for energizing the shunt relay 58H. Such decrease of course causes both the track relay 5TR andthe relay 5SH to cease operation because the energy in these relays has been reduced below their pick-up values. The cessation of intermittent energization of the approach repeating relay EAR results in its dropping away and the closure of back contact I2 to approach light the associated signal in a manner previously described. When the train leaves the track section 5T, normal conditions are restored with relay SSH following the code and relay 5AR picked. The primary feature to be noted with respectto'this Fig. 5 is that a compensating resistor 54 is included in series in the circuit for relay 58H which resisiiir is shunted or un shunted depending upon whether a 180 code or a 75 code is being transmitted. As previously mentioned, a relay fol-lowing a code requires more energy at the fast code rate so that the resistor 54 is shunted by the front contact 5'! so as to supply the relay SSH with more energy during the transmission of the 180 code than. it receives during the transmission of the '75 code. In this way, the effective operation of relay SSH is maintained constant for difierent code rates so as to have more uniform sensitivity'to theentrance of a train into the track section 5T.

Fig. 6 of the accompanying drawings shows a simple series relay having compensation for changesin coder-ate. Inthis Fig. 6, it will be readily appreciated that the operation of the code transmitting relay '60? is atv the r code rate while front contact Eliot relay GHR is closed, but-isatthe 75 code rate while back contact 60 of relay-SHE is closed. Each operationfof the transmitting relay 6GP closes front, contact 6| to applyafcodepulse from the track battery 6 5 through theeseries mesistor 62 -to the rails-cf the traclcasection, dfll foraoperationaof, the code 15 following track relay BTR at the entrance end of the section. The series relay 68B is connected through a series resistor 63 and another series resistor 64 across the opposite terminals of the series resistor 62 while the 75 code rate is being transmitted. But, while the 180 code rate is being, transmitted, front contact 61 is closed, shunting the resistor 64. Each time a code pulse is transmitted, there is a certain potential drop across the series resistor 62 which causes some energy to be applied to the relay GSR. which is insuflicient to operate the relay while no train is in the track section 6T. However, when a train enters the track section T, increased current flow from the track battery 65 is caused so that the potential drop across the series resistor 62 increases to a point suflicient to cause an operating current to flow through the series relay GSR. This opertion of relay 68R causes intermittent closure of front contact 66 and the intermittent energization of the relay EAR to maintain the relay energized closing front contact 24 and effecting the approach lighting of the associated signal in a manner previously described.

The main point to note with respect to this Fig. 6 is that if a 75 code is being transmitted, the front contact 6'! is open to unshunt resistor 64in series with the winding of the relay GSR thus reducing the energy supplied to this relay for its operation. In other words, this form of the invention illustrates how a change in code rates can act to compensate for the degree of energization required to operate a simple series approach relay.

From the above description of the several figures of disclosure, it will be seen that the various characteristic features of the present invention may be employedin combination with each other or may be used separately under varying conditions and circumstances of actual practice. However, these features when combined to provide a composite approach control organization, as disclosed in the preferred forms of the present invention, result in a highly efiective and efiicient approach control organization giving a substantial increase in the length of track circuits that can be used in connection with such control and still provide for approach lighting of an advance signal immediately upon an entrance of a train into the associated track section. However, as above mentioned, it is not essential in the practice of the invention to have the approach control zone extend throughout the length of its associated track section because some coded track sections are longer than required for approach lighting. Insuch cases, however, the effective control zone is greatly increased over that which is capable of being provided by the usual conventional approach control organization.

Having described several forms of a coded track circuit automatic block'signalliri ..system, employing approach control apparatus organ ized to give increased sensitivity, as embodying the principles'of the present invention, it is desired to be "understood that the invention'is shown in this connection andin' this manner for the purpose of facilitating the disclosure, and that the invention may be applied to various other applications of coded track circuits. It is to be further understood that the specific em bodiments of the present invention may have various modifications, adaptations and alterations m adelto the forms shown to meet the re- 16 quirements of practice, without in any manner departing from the spirit or scope of the present invention except as limited by appended claims.

What I claim is:

'1. In a coded track circuit for railroads, the combination with a source of current and coding means for intermittently connecting said source across the track rails at one end of a track section, an approach relay at said one end having two differential windings and biasedv polar armature, means for connecting one winding of said approach relay across the track rails at said one end, and means for independently steadily energizing the other winding of said approach relay from said source of current to provide a magnetic biasing effect tending to operate said polar armature to its biased position.

2. In a coded track circuit for railroads, a source of current and limiting resistance associated with a track circuit, means including coding contacts for intermittently connecting said source of current in series with said resistance across the track rails at one end of said track circuit to energize it with code pulses, a differential approach relay of the biased polar type having one winding energized from the track rails at said one end by the code pulses applied thereto, and circuit means for connecting the other winding of said approach relay across said source of current alone to provide a substantially uniform flux in said relay tending to move the polar armature of said relay to its biased position.

3. In a coded track circuit for railroads, code transmitting and approach control apparatus at one end of the track circuit comprising a source of energy and a limiting resistor, coding means for intermittently connecting said source of energy and said resistor in series across the track rails to transmit code pulses over the track circuit, control means governed in accordance with traffic conditions for causing said coding means to operate at different selected rates, an

approach relay, a compensating resistor connected in series with said approach relay, circuit means including said, compensating resistor for supplying said approach relay with current in accordance with the potential of the code pulses supplied to the track circuit, and means governed by said control means for changing the value of said compensating resistor in accordance with the selected code rate.

4. In a coded track circuit for railroads, the combination with a source of current and coding means for intermittently connecting said source of current across the track rails at one end of a track section to transmit code pulses, an approach relay having a main windin and a differential compensating winding associated with a biased polar armature, means for energizing said main winding in accordance with the code pulses applied to said track section for causing the operation of said polar armature to be dependent upon the presence and absence of a train in the track section, means for independently and steadily energizing the other winding of said approach relay to provide a steady mag:

netic biasing eiiect tending to operate said polar armature to its biased position, and means associated with said coding means for at times changing the degree of energization of said compensatin winding.

5. In 'a coded track circuit for railroads, a track section having a track relay connected at one end and code transmitting means at the other end comprising a source of :current' and coding contacts for intermittently connecting said source of current across the track rails at said other end of said track section, an approach relay at said other end having a main winding and a differential compensating winding associated with a polar armature biased to one position, means for energizing said main winding of said approach relay in accordance with the energization of said track rails by said coding means from said source, and means for independently energizing the, compensating winding of said approach relay with a steady energization from said source of currentto provide a steady magnetic bias eifect tending to operate said polar armature to its biased position.

6. .In a coded track circuit for railroads, the combination with a, source of current and coding, means for intermittently connecting said source of current across said track rails at one end ,ofa, track section, an approach relay having two windings and a biased polar armature, meansv for connecting one winding of said, approach relay across the track rails of said section at said,

one end so as to be intermittently energized from said source, and means for independently steadily energizing the other winding of said approach relay from said source of current to provide a magnetic flux opposing the magnetic flux produced by the energizationof said main winding but being of a smaller degree to only tend to operate said polar armature to its biased position, whereby said approach relay is rendered more sensitive to a train shunt on said track section.

7. In a coded track circuit for railroads, a track section having a code following track relay at one end and code transmitting means at the other end including a source of current, coding contacts operated intermittently at diiferent rates, an approach relay, means for connecting said source intermittently across the track rails at said other end of said track section at different selected rates, circuit means for supplying said approach relay with energy during said. pulses in accordance with the current supplied to said track section, control means for governing said code transmitting means to select a different code rate in accordance with traific conditions, and steadily energized electrical biasing means governed by said control means for changing the operatin current values of said circuit means for said approach relay in-accordance with the selected code rate.

8. In a coded track circuit for railroads, a track section having a code following track relay at one end and' code-transmitting means at the other end, said code transmitting means including a source of current and coding contacts operating intermittently for applying code pulses to the track rails at that end of the track section at one selected code-rate, control means forgoverning said coding means to select a diiferent code rate in accordance with traffic conditions, an approach relay of the biased polar type and having a main winding connected across the track rails at said other end of said track'section so as to be responsive to the code pulses applied to said track section at that end, said approach relay also having a steadily energized compensating winding, and means governed by said control means for changing the degree of energization of said compensating winding dependent upon a change in the selected code rate.

9. In a coded track circuit for railroads, a coding means including a source of current and oding c n a ts t o e. n of a rack se tion.

aid c i g ans pe tin o pply od ul es across the track rails at different selected rates in accordance, with traific conditions, control means for governing said coding means toselect traclc section, and also having a compensating winding, and means governed by Said control means for changing thedegree of energization of said compensating winding of said approach re layin accordance, with the dififerent selected code rates.

10. In a coded track circuit for railroads, a track section, a source of rectified alternating current and a reverse battery connected in multiple therewith at one end of said track section,

code transmitting means at said one end of said section for intermittently connecting said source and. said battery across said track rails" to apply d code pulses at a rate selected in accordance with "traffic in advance, an approach relay of the biased polar type associated with said one end.

of said track section and having a main winding and a compensating winding, said main winding being associated with that end of said track section so as to be responsive to the presenceof a train in that track section, and means includ-,

ing a power-off relay responsive to the failure of l ing means at one end of a track section including a battery source of energy and acting to inter? mittently apply code pulses to the track rails at that end at a, rate selected in accordance with traffic conditions, an approach relay associated with said one end of said track section and having a main winding and asteadily energized coma pensating winding energized from said source, said main winding being connected across the track rails of said section at said one end, and

a regulating means responsive to changes in the voltage applied to the track railsfrom said source for changing the degree of energization of said difierential winding of said approach relay as variations in the potential of said battery source occur.

12. In a coded trackv circuit for railroads,co d ing means including a source of rectified alter-1 natingcurrent and a reserve battery connected in multiple therewith for intermittently applying code. pulses to the. track rails atone end ofa track section for energizing a code following track relay at the other end of the track section inaccordance with traflic conditions, an approach relay associated with said one end of said track section and having a main winding and a conipensating winding, a power-off relay responsive 19 source" of supply and a multiple connected floating battery for supplying energy to the track rails of a track section at one end for energizing a track relay at the other end, an approach relay connected across said track rails at said one end, a power-off relay responsive to the failure of alternating current supply, a regulating relay connected across said battery only when said power-off relay is deenergized upon failure of the alternating current supply, means for changing the operating current requirements of said approach relay as the energization of the track circuit is changed from the rectified alternating current to the reserve battery as indicated by said power-off relay and as the energization of the track circuit is changed upon the falling 011 of the voltage of said battery as indicated by said regulating relay.

14 .'lna tracK circuit for railroads, the comb'ination with a primary battery for applying energy to the track rails of a track section at one end and for energizing a track relay at the other end, an approach relay having two windings one connected across said track rails at said one end, a regulating relay connected to said battery and responsive to variations in its voltage, and circuit means governed by said regulating relay for changing the degree of energization of the other winding of said approach relay dependent upon the voltage of said source.

15. in a coded track circuit for railroads, a source of current and a series limiting resistance associated with the exit end of a track section, means including coding contacts for intermittently connecting said source of current in series with said resistance across the track rails at said one end, an approach relay associated with said exit end of said track section and having two windings, means for connecting one winding across the track rails so as to be energized by said code pulses, and circuit means for connecting theother winding of said approach relay across said source of current for energiz ing it to a limited degree to provide a steady opposition to the intermittent energization of said one winding, whereby said approach relay is rendered more sensitive to the entrance of a train into said track section.

16. In a coded track circuit for railroads, a

source of current and a limiting resistor associated with the exit end of a track section, coding contacts operating to intermittently connect said source of current'in series with said resistor across said track section to apply code pulses of selected rates to said track section, control means for governing said coding means to select the-different code rates in accordance with traffic conditions, an approach relay having a winding connected across the rails of said track section so as to be energized by the code pulses and to be responsive to the entrance of a train into a corresponding track section, and means governed by said control means for changing the effective energizationof said approach relay in accordance with the difierent selected code rates.

17. In a coded track circuit for railroads, a source of current and a limiting resistor associated with one end of a track section, code transmitting means for intermittently connecting said source of current and said resistor in series across the track rails of the'tracksection to apply code pulses in accordance with diiferent selected code rates, control means for governing said code transmitting means to select the different code rates, an approach relay having a winding connected across the terminals of said limiting resistor so as to be effectively energized only when a train enters said track section, and means governed by said control means for changing the 6 eiiective degree of energization of said approach relay dependent upon the different selected code rates.

'18. In a coded trackcircuit for railroads, a

track circuit section having code receiving means giconnected to its rails at one end, a source of current and a limiting resistance associated with the other end of the section, code transmitting contacts for intermittently connecting said source of current inseries with said resistance 65 across the rails of said section for applying code pulses thereto at diflerent selected rates, an approach relay having a winding connected to the coded track circuit of said section at said other end so as to be normally responsive to the inyter-rail potential during the application of said code pulses to thereby operate its contacts at a rate corresponding to the rate of said code pulses but to cease such operation when said section is shunted by a train, control means for selecting the rate of operation of said code transmitting contacts in accordance with traflic conditions, and means also governed by said control means for modifying the effective energization of said approach relay in accordance withthe selected code rate, whereby said approach relay is caused to follow the code pulses with the same degree of lag regardless oftheir different rates.

19. In a codedtrack circuit for railroads, a source of current, a series resistor, and coding contacts acting intermittently to connect said source and said series resistor to apply energy to the track rails of a track section at one end for intermittently energizing a track relay at the other end with code pulses, an approach relay having a winding energizable in accordance with the inter-rail potential of said track. rails at said one end, a regulating relay connected to said source and responsive to variations in its voltage,

and means governed by said regulating relay for modifying the efiective energization of said approach relay dependent upon the variations in voltage of said source.

' JAMES Y. HOWARD.

REFERENCES CITED file of this patent:

UNITED STATES PATENTS The following references are of record in the 

